SiO2f/SiO2 composites offer excellent dielectric and thermal stability, but reliable integration remains difficult due to the limitations of conventional metal brazes, including CTE mismatch and electrical conductivity. This study developed a novel all-dielectric brazing material, Bi2O3-B2O3 (BB) glass, for joining SiO2f/SiO2 composite materials. The BB glass synthesized via melt-quenching exhibits an amorphous structure, a low glass transition temperature (Tg=403 °C), and an adjustable CTE (7–9 × 10–6/ °C). Wetting experiments demonstrate excellent spreading on the SiO2f/SiO2 surface, with a contact angle as low as 16° Density functional theory (DFT) analysis reveals that the formation of Bi-O-Si bonds and B-O-Si networks at the interface enhances the bonding strength. Differential charge density and density of states (DOS) results indicate that the electronic structure of BB glass improves dielectric response and reduces insertion loss in the GHz frequency band. BB glass overcomes the shortcomings of traditional brazing materials, providing a theoretical and technical foundation for reliable joining of SiO2f/SiO2 composite materials in extreme environments.

Ceramics and ceramic-based composites have been widely used in electronic information and communication, chemical industry, instrument manufacturing and other fields. However, due to the brittleness and processability of ceramic materials, ceramics need to be connected with metal materials to meet practical applications. Among various bonding methods, brazing is widely used for joining ceramics and metals. However, due to the difference in the properties of ceramics and metals, especially the coefficient of thermal expansion, excessive residual stresses are generated in the joint subject to deformation during the cooling process of the brazed joint. High residual stresses can seriously damage the joint properties. To relieve residual stresses, this review has summarized three residual stress relief methods: particle reinforcement, interlayer assisted control, and surface structure design. These methods can effectively relieve stress concentration in joints, improve joint plasticity, and reduce the ceramic-metal discrepancy, thus leading to the enhanced performances. Finally, the future opportunities and challenges of regulation strategy for releasing residual stress are also presented. Overall, it is expected that these stress relief strategies will provide some new understanding of the wide range of applications for ceramic-to-metal joints.

To expand the application of SiO2f/SiO2 composites, joining is one indispensable process. However, it is hard to take care of the property of the composites and simultaneously form a robust joint. Here, a B2O3-ZnO glass filler with a loose network structure was designed to realize the self-joining of SiO2f/SiO2 composites. Results revealed that silica has a relatively rapid diffusion rate in B2O3-ZnO glass which is beneficial for the fast replacement of the glass network former. After brazing, silica diffused into the brazing seam, became a new network former and thus regulated the glass network structure. As a result, the maximum working temperature of the joint increased 200 degrees C compared with pristine B2O3-ZnO glass. The joints own 23.3 MPa shear strength at room temperature and remain 22.3 MPa at 600 degrees C. This work offers a way to achieve the joining of SiO2f/SiO2 composites and break through the original maximum working temperature of the glass filler.

Joining is an indispensable process for expanding the application of ceramics and composites. Recently, glasses have been extensively explored for ceramic/composite joining owing to their unique functional needs. However, the difficulty in detecting amorphous materials and lack of enthalpy data make the interfacial reaction mechanism challenging to investigate. In this study, the interfacial reaction mechanism of joints of SiO2f/SiO2 composite-brazed bismuth glass was thoroughly explored. SiO2 was dissolved from the matrix and used throughout the brazing process. In the initial stage, silica reacts with the brazing glass to form Bi4(SiO4)3. Then, owing to the decomposition of Bi4(SiO4)3, the silicate glass replaced the bismuth glass. Finally, some precipitation of SiO2 occurred at the brazing seam owing to an entropy–enthalpy dominating mode. This study may instigate the design of brazing glasses for joining SiO2f/SiO2 composites.

Nowadays,SiO2 based material is one of the widest used materials in optical,microelectromechanical system,aerospace and some other industries.In practical application,SiO2 based materials are required to be joined with themselves or other heterogeneous materials to assemble products with various func-tions.And the joining quality directly affects the mechanical performances and functional properties of assembled products.Though many researchers studied different joining technologies,explored the mi-crostructure of joining interface and tested after-joining properties,a review that summarizes the re-cent cutting-edge researches and development tendency of joining technologies for SiO2 based ceramics is still absent.Therefore,according to different applications and requirements,this review summarizes the widely used joining technologies and discusses corresponding joining mechanisms,current research progress and suitable applications.Due to the wide applications in specific industry,laser welding,an-odic bonding and wafer bonding are discussed in detail.Further,brazing,the widest used method in SiO2 joining,has been elaborated deeply in its wetting mechanism,residual stress control,interfacial microstructure and mechanical performance aspects.In the end,this review proposed the future devel-opment trends of SiO2 ceramics joining,aiming at offering a full-view of potential improvements in SiO2 ceramic joining technologies.

Reliable Si3N4/Si3N4 joints is successfully prepared in air using pure Al filler. The interfacial microstructure, phase composition and mechanical properties of the joint are investigated in detail. The effects of joining temperature on joint structure and mechanical properties are studied. The experimental results indicate that the diffusion occurs at the interface between Si3N4 ceramics and Al filler. A maximum shear strength of similar to 42 MPa is obtained for joints joining at 950 degrees C for 1 h. The work makes an attempt on the joining of Si3N4 ceramics in air, which broadens the joining method of Si3N4 ceramics.

To extend the application of the SiO2f/SiO2 composites, self-joining process is indispensable. Reliable self-joining of SiO2f/SiO2 composites was achieved by Bi2O3-B2O3-ZnO glass. With a low glass transition temperature, the onset temperature of residual stress is much lower than that of active brazing. In addition, bismuth glass exhibits a good wettability on the surface of SiO2f/SiO2 composites. When the joints were brazed at 750 degrees C/30 min, the average shear strength of the joints reached 21.2 MPa, reaching 77.8% of the shear strength of SiO2f/SiO2 composites. This technology can effectively fill the bank of self-joining of SiO2f/SiO2 composites.

Constructing well-defined nanointerfaces is vital to enhance the catalytic performances through electronic coupling effects from different components. However, it is still a challenge to construct metal selenides-based interfacial nanomaterials with satisfactory oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) performances for overall water splitting. Herein, sandwich-like structured NiSe2/Ni2P@FeP nanosheet arrays are rationally constructed, which starts from NiSe2 arrays directly on carbon cloth as backbones, followed by coating FeP nanoparticles on the backbones through the phosphorization process. Further, abundant nanointerfaces with rich defects and disordered structure are constructed during the phosphorization process, which can boost the charge transfer rate and provide rich electroactive sites. Consequently, as-synthesized NiSe2/Ni2P@FeP nanosheet arrays exhibit good HER and OER performances with small overpotentials, low Tafel slopes and good stability. Further, the overall water splitting device built by NiSe2/Ni2P@FeP exhibits a voltage of 1.554 V to attain 10 mA cm(-2). Our current work may provide some new insights on rationally constructing nanointerfaces with rich defects to boost the catalytic performances for overall water splitting.

Element doping is a general and effective approach to modify the electrocatalytic performances, but the low intrinsic activity in each electroactive site still limits the further improvements. Herein, we provide an effective strategy by simultaneously introducing P doping and Se vacancies to enhance the intrinsic activities in NiSe2 nanosheet arrays (A-NiSe2 vertical bar P) through Ar plasma treatment. Owing to the increased active sites and enhanced electrical conductivity, the resulted A-NiSe2 vertical bar P shows the enhanced hydrogen evolution performances. Theoretical calculations reveal that introduction of Se vacancies plays a significant role in lowering the adsorption free energy of H* in Ni, Se and P sites, leading to promoted intrinsic activities in A-NiSe2 vertical bar P. Further, A-NiSe2 vertical bar P as bifunctional electrocatalysts only needs 1.62 V to reach 10 mA cm(-2) for overall water splitting. Our study and understanding of A-NiSe2 vertical bar P may highlight the importance of element doping and vacancies in enhancing the catalytic activities in overall water splitting. (C) 2020 Elsevier Inc. All rights reserved.

Rational design and fabrication of advanced electrodes with tailored functionality is of great significance for high-performance asymmetric supercapacitors. Herein, we report the preparation of Fe2O3 nanotube arrays and core-branch NiO nanotube arrays directly on carbon paper by using ZnO nanorods as sacrificial templates via similar synthesis process, which works anode and cathode electrodes for the asymmetric supercapacitors. Benefiting from the free-standing nanotube nanostructures, a large number of surface active sites and fast ion diffusion paths, the Fe2O3 and NiO electrodes could achieve the high capacity up to 81.9 mAh g(-1) and 119.7 mAh g(-1), respectively. Further, an asymmetric supercapacitor is also assembled by using Fe2O3 as anode and NiO as cathode, which shows a high energy density of 48Wh kg(-1) at the power density of 2089 W kg(-1). Current research may put a general route for constructing high-performance anode and cathode materials in energy storage devices. (c) 2019 Elsevier B.V. All rights reserved.

Owing to low-cost and 3d electronic configurations, Co3O4 material is considered as promising candidate for oxygen evolution reaction (OER) electrocatalyst, but the intrinsically low conductivity and limited active site exposure greatly limit the electrocatalytic performances, Herein, we successfully achieve modulation of Co3O4 arrays by Mn and S dual-doping for OER. Results demonstrate that Mn doping modifies the electronic structure of Co center to boost the intrinsic activity of active site in Co3O4, while inducing S in Co3O4 increases the electrical conductivity and provides ample S sites for proton adsorption. In addition, Mn and S dual-doping effectively increase the proportion of Co3+, resulting in facilitating the four-electron transfer and thus higher electrochemical activities. Consequently, the optimal Mn and S dual doping Co3O4 presents low overpotentials of 330, 407 and 460 mV at 10, 100 and 300 mA cm(-2) for OER, as well as a low Tafel slope of 68 mV dec(-1) and a good durability after 20 h. Current work highlights a feasible strategy to design electrocatalysts via dual-doping and maximizing the high-valence transition metal ions. (C) 2019 Elsevier Inc. All rights reserved.

Designing and constructing bifunctional electrocatalysts is vital for water splitting. Particularly, the rational interface engineering can effectively modify the active sites and promote the electronic transfer, leading to the improved splitting efficiency. Herein, free-standing and defect-rich heterogeneous MoS2/NiS2 nanosheets for overall water splitting are designed. The abundant heterogeneous interfaces in MoS2/NiS2 can not only provide rich electroactive sites but also facilitate the electron transfer, which further cooperate synergistically toward electrocatalytic reactions. Consequently, the optimal MoS2/NiS2 nanosheets show the enhanced electrocatalytic performances as bifunctional electrocatalysts for overall water splitting. This study may open up a new route for rationally constructing heterogeneous interfaces to maximize their electrochemical performances, which may help to accelerate the development of nonprecious electrocatalysts for overall water splitting.

Constructing high-efficiency electrocatalysts is vital towards electrocatalytic water splitting, but it remains a challenge. Although Ni-based materials have drawn extensive attention as highly active catalysts, the relatively limited electroactive sites in Ni-based catalysts still remains a great issue. In order to further boost the electrocatalytic performances, heteroatom doping and interface engineering are usually adopted for modification. Here, a new strategy is developed to construct W doped NiO/NiS2 interfaced nanosheets directly on carbon sheet, which is working as efficient and bifunctional electrocatalysts for overall water splitting. W doped NiO nanosheets are directly constructed on the carbon sheet by the hydrothermal and annealing processes. After that, W-NiO was subjected to Ar plasma assisted sulfuration treatment for forming W doped NiO/NiS2 interfaced nanosheets. Based on systematic investigations, we find that W doping can effectively induce the modified electronic structure of Ni to boost the intrinsic activities in NiO/NiS2. Further, forming NiO/NiS2 nanointerfaces can also provide rich electroactive sites and boost the charge transfer rate. Consequently, W doped NiO/NiS2 exhibits the much enhanced performances for overall water splitting. As a bifunctional electrode, W-NiO/NiS2 demonstrates a remarkable activity with a 1.614 V cell voltage at 10 mA cm(-2) for overall water splitting. (C) 2019 Elsevier Inc. All rights reserved.

Rational design of efficient bifunctional electrocatalysts is highly imperative but still a challenge for overall water splitting. Herein, we construct novel freestanding Mo-doped NiCoP nanosheet arrays by the hydrothermal and phosphation processes, serving as bifunctional electrocatalysts for overall water splitting. Notably, Mo doping could effectively modulate the electronic structure of NiCoP, leading to the increased electroactive site and improved intrinsic activity of each site. Furthermore, an electrochemical activation strategy is proposed to form Mo-doped (Ni,Co)OOH to fully boost the electrocatalytic activities for oxygen evolution reaction. Benefiting from the unique freestanding structure and Mo doping, Mo-doped NiCoP and (Ni,Co)OOH show the remarkable electrochemical performances, which are competitive among current researches. In addition, an overall water splitting device assembled by both electrodes only requires a cell voltage of 1.61 V to reach a current density of 10 mA cm−2. Therefore, this work opens up new avenues for designing nonprecious bifunctional electrocatalysts by Mo doping and in situ electrochemical activation.

Herein, a general strategy is provided to construct N-doped carbon-confined MoO2 and MnO by the hydro thermal process, polymerization process and carbonation process, which serves as negative electrode and positive electrode for hybrid supercapacitors. The N-doped carbon as shell can provide fast electron pathways and short ion diffusion paths, resulting in the improved performances at the high rates. Consequently, the obtained N-doped carbon-confined MoO2 and MnO possess the good electrochemical performances, including high specific capacitance, excellent cycling stability and good rate capability. Furthermore, the as-fabricated hybrid supercapacitor using N-doped carbon-confined MoO2 and MnO shows a high energy density up to 44.82 Wh kg(-1) at a power density of 900 W kg(-1), as well as good cycling performance. This work may provide a general strategy for constructing high-performance energy storage devices.

The electrochemical performance of nanostructured nickel-cobalt sulfides is greatly limited by the sluggish reaction kinetics and limited electroactive sites. Herein, we design and synthesize free-standing Se doped nickel cobalt sulfides with controllable-component directly on carbon cloth, which involves the hydrothermal process and sulfuration/selenylation reaction. Serving as free-standing electrode, as-synthesized Se doped nickel-cobalt sulfides not only favor the fast ion diffusion path and low contact resistance, but also provide rich electroactive sites with electrolyte. More importantly, proper Se doping in nickel-cobalt sulfides greatly increases the electrochemically active surface area and reduces the charge transfer resistance. Based on the X-ray photoelectron spectroscopy and transmission electron microscopy results, the reaction mechanism is convincingly revealed that Se dopants have been changed into SeOx. And electrochemical activated oxyhydroxides are mainly involved in electrochemical reactions. As a result, as-fabricated Se doped nickel-cobalt sulfides show a good electrochemical performance for supercapattery. Further, the supercapattery device is also assembled by using nickel-cobalt sulfide/selenide as positive electrode and activated carbon as negative electrode, which shows a high energy density of 39.6 Wh kg(-1) at the power density of 1501 W kg(-1).

We report a facile synthesis strategy for core-branched CoSe2/Ni0.85Se nanotube arrays directly on Ni foam by simply selenizing Co-precursor nanowires.

Brazing SiO2-BN with Ti6Al4V is often associated with the problems of high residual stress and excessive Ti-based compounds formed. To overcome these problems, we report a new type interlayer of carbon nanotube (CNT) reinforced Ni foam fabricated by plasma enhanced chemical vapor deposition. The in-situ grown CNT are homogenously dispersed on 3D structure Ni foam, which could effectively avoid damage and agglomeration in the brazing seam. Result shows that Ni foam could consume excessive dissolved Ti, and CNT was beneficial for restricting the growth of phase, improving joining strength and releasing residual stress rapidly. The average shear strength of the joint brazed with CNT-Ni foam is about 50MPa, and this value is about 5 times higher than that of joints brazed with pure TiZrNiCu. Further, a new simulated experiment was carried out innovatively to solving the difficulty of investigating interfacial behavior of CNT in brazing seam. Then the results clarify that integral structure of CNT can prevent the reaction with Ti. In situ growth of CNT on Ni foam could provide a way for introducing CNT into brazing seam without damaging structure of CNT.

CF/PEEK composites were welded assisted by ultrasonic. The influence of vibration time and using of energy director (ED) to the joints were investigated in details. The joints had defect of incomplete fusion at the interface under short welding time without ED, and defects of cracks and voids appeared at the interface of carbon fiber and PEEK resin, which attributed to too much heat accumulation at the heat affected zone (HAZ). By using flat ED, joint with sound bonding was realized under vibration time of 0.9 s. The lap shear strength of joint can reach 28 MPa, and the joint fractured at the HAZ. The real-time temperature at interfaces were monitored. It is found that the heating rate can be accelerated by using flat ED, and the peak temperature was lowered. At last, the influence mechanism of processing parameter to the joint were discussed in details.